Search

The first objective of this work was to evaluate the ability of the long-term BOD tests to provide the total biodegradable COD (BCOD) for domestic wastewaters. Results show that the method is repeatable (using two different volume samples, 97 and 164 mL) and that the fractions of BCOD determined were not statistically different from the one obtained by respirometry (at low S/X ratio). Respirometric tests were also repeatable. They were shown to be sensitive to the origin of the sludge. The results obtained are in the range of literature data. But they later indicated that long-term bioassays (>20 days) give higher biodegradable fractions than the other methods (BOD and respirometry). The second objective was to compare soluble fractions obtained with raw and pre-flocculated samples. Flocculated filtered COD is significantly lower than filtered COD, even if a pore size of 0.1 mm is used. The comparison to literature values shows that physicochemical RBCOD fractions are significantly higher than the ones obtained using bioassays. Comparison with the fractions used in calibrated models would help the choice of the more suitable method for modelling purposes. [ABSTRACT FROM AUTHOR]

This paper serves as a problem statement of the issues surrounding uncertainty in wastewater treatment modelling. The paper proposes a structure for identifying the sources of uncertainty introduced during each step of an engineering project concerned with model-based design or optimisation of a wastewater treatment system. It briefly references the methods currently used to evaluate prediction accuracy and uncertainty and discusses the relevance of uncertainty evaluations in model applications. The paper aims to raise awareness and initiate a comprehensive discussion among professionals on model prediction accuracy and uncertainty issues. It also aims to identify future research needs. Ultimately the goal of such a discussion would be to generate transparent and objective methods of explicitly evaluating the reliability of model results, before they are implemented in an engineering decision-making context. [ABSTRACT FROM AUTHOR]

The objective of this work was to analyse the impact of different geometric and operating parameters on the alpha factor value for fine bubble aeration systems equipped with EPDM membrane diffusers. Measurements have been performed on nitrifying plants operating under extended aeration and treating mainly domestic wastewater. Measurements performed on 14 nitrifying plants showed that, for domestic wastewater treatment under very low F/M ratios, the alpha factor is comprised between 0.44 and 0.98. A new composite variable (the Equivalent Contact Time, ECT) has been defined and makes it possible for a given aeration tank, knowing the MCRT, the clean water oxygen transfer coefficient and the supplied air flow rate, to predict the alpha factor value. ECT combines the effect on mass transfer of all generally accepted factors affecting oxygen transfer performances (air flow rate, diffuser submergence, horizontal flow). [ABSTRACT FROM AUTHOR]

Abstract: The standard oxygenation performances of fine bubble diffused aeration systems in clean water, measured in 12 cylindrical tanks (water depth from 2.4 to 6.1m), were analysed using dimensional analysis. A relationship was established to estimate the scale-up factor for oxygen transfer, the transfer number The transfer number, which is written as a function of the oxygen transfer coefficient , the gas superficial velocity , the kinematic viscosity of water and the acceleration due to gravity , has the same physical meaning as the specific oxygen transfer efficiency. only depends on the geometry of the tank/aeration system [the total surface of the perforated membrane , the surface of the tank or its diameter , the total surface of the zones covered by the diffusers (“aerated area”, ) and the submergence of the diffusers ]. This analysis allowed to better describe the mass transfer in cylindrical tanks. Within the range of the parameters considered, the oxygen transfer coefficient is an increasing linear function of the air flow rate. For a given air flow rate and a given tank surface area, decreases with the water depth (submergence of the diffusers). For a given water depth, increases with the number of diffusers, and, for an equal number of diffusers, with the total area of the zones covered by the diffusers. The latter result evidences the superiority of the total floor coverage over an arrangement whereby the diffusers are placed on separate grids. The specific standard oxygen transfer efficiency is independent of the air flow rate and the water depth, the drop in the being offset by the increase of the saturation concentration. For a given tank area, the impact of the total surface of the perforated membrane and of the aerated area is the same as on the oxygen transfer coefficient. [Copyright &y& Elsevier]

In various cases in environmental modeling, modelers need to account for multiple variables and multiple objectives in systems with many processes occurring at different time scales. To assist the modeler to choose a relevant pool of efficiency criteria, a method is proposed to identify dissimilar criteria. A total of 30 efficiency criteria used in environmental modeling are critically reviewed and classified into six groups according to different modeling objectives. After accounting for equivalence of functional form 18 criteria remain for further analysis. To quantify the dissimilarity for the remaining criteria a methodology based on the ratio of shared parameter sets in regions of good performance is proposed. Then, for a wastewater treatment plant case-study the dissimilarity of efficiency criteria is analyzed as a function of target variables and operating conditions. [ABSTRACT FROM AUTHOR]